A conventional orthogonal frequency division multiplexing (OFDM)-based signal transmitting apparatus and a conventional OFDM signal receiving apparatus will be described with reference to FIG. 1.
FIG. 1 is a block diagram of a conventional OFDM-based signal transmitting apparatus 10 and a conventional OFDM-based signal receiving apparatus 20.
As shown in FIG. 1, the conventional OFDM-based signal transmitting apparatus 10 includes a digital modulator 11, a serial-to-parallel converter (SPC) 12, an inverse fast Fourier transform (IFFT) operator 13, a parallel-to-serial converter (PSC) 14, a cyclic prefix (CP) adder 15, a digital-to-analog converter (DAC) 16, a transmission unit 17, and a transmit antenna 18.
The digital modulator 11 digital-modulates a data symbol to be transmitted through a channel and generates a digital modulation symbol, the data symbol formed of binary data. The digital modulation performed by the digital modulator 11 includes binary phase shift keying (BPSK) modulation, quadrature phase shift keying (QPSK) modulation, quadrature amplitude modulation (QAM), 16-QAM, and 64-QAM. The digital modulator 11 is also referred to as a symbol mapping unit.
The SPC 12 serially receives a plurality of digital modulation symbols from the digital modulator 11 and outputs the received digital modulation symbols in parallel.
The IFFT operator 13 performs an IFFT operation on the parallel digital modulation symbols output from the SPC 12 and generates a plurality of IFFT symbols.
The PSC 14 receives the plurality of IFFT symbols output from the IFFT operator 13 in parallel, and serially outputs the IFFT symbols.
The CP adder 15 adds a CP signal in front of each of the IFFT symbols serially output from the PSC 14 and generates a symbol group to which the CP is added. Herein, the CP signal is a copy of a last portion of each of the plurality of IFFT symbols.
The DAC 16 receives the symbol group to which the CP is added from the CP adder 15, converts the symbol group into an analog signal, and generates one OFDM symbol.
The transmission unit 17 amplifies the OFDM symbol generated by the DAC 16 into a radio frequency (RF) signal and transmits the RF signal to a channel through the transmit antenna 18.
As shown in FIG. 1, the conventional OFDM-based signal receiving apparatus 20 includes a receive antenna 21, a receiving unit 22, an analog-to-digital converter (ADC) 23, a CP eliminator 24, an SPC 25, a fast Fourier transform (FFT) operator 26, a PSC 27, and a digital demodulator 28.
The receiving unit 22 receives an OFDM symbol from the channel through the receive antenna 21.
The ADC 23 converts the OFDM symbol received by the receiving unit 22 into a digital signal and generates a plurality of digital symbols.
The CP eliminator 24 eliminates a CP signal from each of the digital symbols generated by the ADC 23.
The SPC 25 serially receives the digital symbols from which the CP is eliminated and outputs the CP-eliminated digital symbols in parallel.
The FFT operator 26 receives the digital symbols output in parallel from the SPC 25, performs an FFT operation, and generates a plurality of frequency domain symbols.
The PSC 27 receives the frequency domain symbols in parallel and serially outputs them.
The digital demodulator 28 digitally demodulates the plurality of frequency domain symbols that have been serially output from the PSC 27 and generates a data symbol.
The OFDM symbol generated through the above-described method has a drawback of having a high peak to average power ratio (PAPR). An OFDM symbol with a high PAPR may experience signal distortion when the OFDM symbol is being amplified by a non-linear device such as a high power amplifier (HPF).
An OFDM-based communication system has such a problem, and therefore various studies have been conducted to improve such a characteristic of the PAPR. However, a method that has been suggested for improving the PAPR characteristic partially uses subcarriers, thereby reducing data transmission speed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.